Democratic Rep. Gerald E. Connolly and Republican challenger Keith Fimian differ on nearly every policy issue and have been squabbling over personal and political matters for well over two years. But they agree on one point: Their race is a tight one.

Just how close is a subject of debate. Fimian and some of his allies claim he is tied with or even ahead of the incumbent, while Connolly's camp and his fellow Democrats are cautiously optimistic that their man will prevail, just as he did when they first squared off in Virginia's 11th Congressional District in 2008.

"It's close . . . without a doubt," Fimian said Tuesday after the candidates appeared at a debate sponsored by the Fairfax County Chamber of Commerce.

Fimian said he was "in the lead," based on his own polling, but neither he nor Connolly nor the national party committees have released a survey in several months.

"I'm feeling pretty good about this race," Connolly said after the debate. But he added, "We can take nothing for granted" as "it's not the kind of favorable climate we faced two years ago."

Whatever the state of the race, both parties are paying increased attention to the drama unfolding just a few miles from Washington. Nonpartisan analysts typically don't rank the contest in the nation's top 40 or 50 most competitive races, but it is increasingly seen as a test case for just how big Republican gains could be in November, given that Connolly beat Fimian by 12 points in 2008 and President Obama won the 11th District by 15 points.

"As the one race actually unfolding within the expensive 'Washington bubble,' this race is a must-win for Democrats hoping to cut suburban losses and hold the House," the nonpartisan Cook Political Report noted last week. "Nervous Democrats know that if they can't gain ground by pounding the GOP candidate as an anti-government, slash-and-burn fundamentalist in northern Virginia''s suburbs, they can't anywhere."

The tension between the candidates was palpable at Tuesday's debate, held at George Mason University.

At one point, Fimian gestured toward Connolly and said: "He will tell you things that are not true. He will tell you things that are outright lies. He will deceive you. . . . He's very good at it."

Asked to respond, Connolly said, "I think the kind of personal ad hominem attack you just heard is what degrades our politics."

He might not be calling Fimian a liar, but Connolly has spent a big chunk of cash in recent weeks going negative.

Connolly spent more than $500,000 for airtime on broadcast television - a more-expensive option than cable - for a spot focused on Fimian's alleged support for an unusual change in the congressional pay scale. The ad shows a clip of Fimian saying: "Cut my salary in Congress to 50,000 bucks, till I balance the budget. But when I balance the budget, I want a $250,000 bonus."

Fimian's campaign said that he was merely making a point about giving lawmakers incentives to do the right thing and that he does not actually support such a change.

Republicans think the ad is an indication that Connolly is running scared.

Nathan L. Gonzales, political editor of the nonpartisan Rothenberg Political Report, said Connolly "probably sees dozens of his colleagues scrambling in competitive races and doesn't want to wake up on November 3 unemployed with a million dollars in his campaign account. By going negative, it looks like Connolly is trying to end the race before Fimian has an opportunity to get traction in the final days."

The Democratic Congressional Campaign Committee has also gotten in on the act, running a Web ad calling Fimian "too extreme" for the district, particularly because of his opposition to abortion.

The committee has spent almost $100,000 on the contest, some of it on mailers saying that Fimian - founder of the home inspection company U.S. Inspect - "falsifies" his business record and has faced a tax lien and lawsuits.

Fairfax County Supervisor Pat S. Herrity's campaign made similar allegations against Fimian during the Republican primary.

Fimian, for his part, has been on local cable stations with an ad pledging that he will create jobs and fight "career politicians" such as Connolly and House Speaker Nancy Pelosi (D-Calif.).

Fimian has run on a strongly conservative platform, criticizing every major bill advanced by the Obama administration - stimulus, "cap and trade," health-care reform and financial regulatory reform. Connolly has sought to chart a more moderate course, backing many Obama initiatives while breaking from fellow Democrats on others.

The divide was on display during Tuesday's debate.

"I am a friend of business. Gerry Connolly is not," Fimian said to the crowd of local business owners and executives, ticking off the list of "anti-business" bills Connolly had supported.

But the two men differed on the merits of those votes.

"You're darn right I voted for the stimulus. . . . I consider that recovery vote one of the most important pro-business votes any of us cast," Connolly said.

Fimian made a broad appeal for change, playing up his outsider status and mostly avoiding references to district-specific issues.

Connolly made a more traditional retail appeal, ticking off his efforts over the years, including his long service on the Fairfax County Board of Supervisors and getting funding for the Dulles Toll Road and the Fairfax County Parkway as well as other local projects.